Print hammer registration control

ABSTRACT

The print quality of a printer is improved by controlling the registration of print hammers as they impact a document and type to print. Variations in print hammer velocity which would affect print registration are compensated for by correspondingly varying the speed of type carrier to maintain proper registration of print hammers and type characters.

United States Patent [19] Gilbert et al.

[ 1 Oct. 22, 1974 PRINT HAMMER REGISTRATION CONTROL [751 Inventors: Richard Lyman Gilbert, Endicott,

Michael David Hryck, Endwell; John Mako, Vestal, all of NY.

[73] Assignee: International Business Machines Corporation, Armonk, NY.

[22] Filed: Mar. 5, 1973 [21] Appl. No.: 338,133

[52] US. Cl 10l/93.4 [51] Int. Cl B4lj 5/22 [58] Field ofSearch 101/93 L; 197/11.1, 16;

[56] References Cited UNITED STATES PATENTS 3,513,774 5/1970 Pawletko et a1. 101/93 C 3,573,589 4/1971 Berry 318/601 3,575,10 4/1971 McDonell et a1. 101/111 X 3,636,867 1/1972 Bonzano 101/93 C Primary Examiner-Robert E. Pulfrey Assistant Examiner-Edward M. Coven Attorney, Agent, or Firm-Francis V. Giolma [57] ABSTRACT Theprint quality of a printer is improved by controlling the registration of print hammers as they impact a ,document and type to print. Variations in print hammer velocity which would affect print registration are compensated for by correspondingly varying the speed of type carrier to maintain proper registration of print hammers and type characters.

5 Claims, 5 Drawing Figures mzmmw zw 230842.736

sum 20? a FIG. 4

BELT SPEED vs. VOLTAGE 7/8 =-KIV BELT SPEED, 80 L /o IN/SEC. ("L/B) v 200 I o I90 o I I Q I I80 IMPACT VELOCITY I L70 I I 2800 160 FLIGHT TIME I I 2000 I50 I I 2400 |40 I I 2 Q l i E 2200 i150 A I I E Q I 5 g 2000 120 I I P? I; o I I I L I800 EH0 A I E g I I 1 I600 :L00 l I 2 i o K2 I I400 90 I I I V I L200 00 I 1 I L000 70 I I I o I I \A\[;3

I T v I 1 I T INPUT POWER---+0 50 I00 I50 200 250 300 350 400 450 PRINT HAMMER REGISTRATION CONTROL BACKGROUND OF THE INVENTION 1. Field of the Invention DESCRIPTION OF A PREFERRED EMBODIMENT Referring to FIG. 1 the reference numeral 10 denotes The invention relates generally to high speed impact 5 generally a Portion of a Printer mechanism wherein an printers and it has reference in particular to printers having electromagnetically operated print hammers and a motor driven type character train or chain.

2. Description of the Prior Art Compensation for differences in flight time between different print hammers in a printer by reason of variations in manufacturing tolerances has been provided by SUMMARY OF THE INVENTION This invention relates generally to printers and it has reference in particular to the control of print registration in printers.

More specifically, this invention provides for controlling the speed of a type carrier in a high speed printer to compensate for changes in flight time of the prin hammers with changes in source voltage.

Another object of the invention is to provide for driving a type chain/train by means of a stepping motor and for varying the frequency of the pulses applied to the stepping motor in accordance with variations in the source voltage.

Yet another object of the invention is to provide for compensating for the effects of source voltage variations on the flight time of a print hammer in a simple and effective manner.

It is also an object of the invention to provide for varying the speed of a type carrier in accordance with variations in source voltage in order to compensate for variations in print hammer flight time caused by variations in the voltage of the print hammer operating source.

The foregoing and other objects, features, and advantages of the invention, will be apparent from the following more particular description of a preferred embodiment of the invention as illustrated in the accompanying drawing:

BRIEF DESCRIPTION OF A DRAWING In the drawing FIG. I is a partial schematic drawing ofa high speed printer embodying the invention in one of its forms;

FIG. 2 is a slightly enlarged side elevational view of a print hammer of FIG. 1;

FIG. 3 is a schematic circuit diagram of the motor control circuit of FIG. 1; 7

FIG. 4 shows a curve illustrating the relation between source voltage and type carrier speed according to the invention, and

FIG. 5 shows curves illustrating the relations between the input power to the print hammer and hammer flight time and impact velocity respectively.

endless type belt 12 is supported on spaced pulleys, of which only one pulley 14 is shown, for moving a plurality of type characters 16 positioned on upstanding fingers 18 on the type belt 12 past a number of print positions along a print line on a document not shown. The type belt 12 contains a plurality of timing marks 20 which are spaced in predetermined relation to the type characters 16 and are sensed by a transducer 21 for controlling the operation of a plurality of print hammers represented by the print hammer 22. The hammer 22 has an operating winding 23 which is energized in timed relation with movement of the type belt 12 through print control means 24 energized from a source of electrical energy over conductors 28. The type belt 12 is operated by means .of a motor 30 which is connected in driving relation with the pulley l4 and is energized through a motor control circuit 32 also connected to the source through conductors 28.

The motor 30 may comprise a stepping motor which is operated by means of pulses applied to the operating windings thereof. The stepping motor 30 may be of the type described in the article entitled Characteristics of a Synchronous Conductor Motor by Arthur E. Snowdon and Elmer W. Madsen, published in Applications and Industry, March, 1962 after being the subject of paper 61-650 recommended by the AIEE Industrial Control Committee and approved by the AIEE Technical Operations Department for presentation at the AIEE Northeastern District Meeting, Hartford, Conn. May 17-19, 1961. Such a motor has a speed proportional to the rate at which pulses are appliedto it, and is normally substantially unaffected by variations in the value of the source voltage.

As shown in FIG. 2 the print hammer 22 may comprise an armature 34 pivotally supported by a pivot 35 an having an upstanding extension 36 with a hammer face 38 at the upper end for impacting the type characters 16. A substantially u-shaped magnet core 40 is provided having the operating winding 23 mounted on the lower leg which terminates within the winding so that a hooked end portion 42 of the armature 34 projects into the winding.

Referring to FIG. 3 it will be seen that the motor control circuit 32 comprises a pair of triggers 42A and 42B connected to operate as a binary counter in response to input pulses from an oscillator 44. The outputs of the triggers 42A and 42B are connected to AND circuits 46A, 46A, 46B and 46B which are connected to the terminals A, A, B and E of the motor 30 respectively.

The oscillator 44 may be of any suitable type comprising for example a well-known relaxation oscillator which includes in its circuit a capacitor 48 which is charged and discharged to provide the oscillator function and determine the frequency of oscillation. The capacitor 48 may be charged from a current source represented by-a transistor 50 which is connected to a source of direct current through conductors 28, fixed resistors R15 and R18, and variable resistor R17, which may be adjusted to vary the charging rate of the capacitor 48. Resistor R16 and capacitor C16 provide a stabilizing filter. The base of the transistor 50 is connected to the source through a bias network including diodes D2, D10, and D11 and resistor R19. A resistor R20 is connected in shunt with the diodes, and this circuit provides the base drive for the transistor 50.

A ramp generator 52 including a capacitor 53 is connected to the base of 'the transistor 50 through a resistor R21, for initially biasing the transistor 50 off, and permitting it to gradually conduct so that a delay is prosite occurs. Accordingly the speed of the stepping vided during which themotor 30 may pick up to its running speed. The ramp generator 52 is turned on by application of a Belt Run signal at terminal 54. A Belt Gate signal is applied to the AND circuits 46A, 46A, 46B and 4613, for controlling the operation of the motor 30 independently of the oscillator 44.

Without compensation a plus or minus 10 percent change in the nominal valueof the 24 volt DC supply would cause more than 150 microseconds change in the flight time of the print hammer. This would cause visible character misregistration. If the print hammer 22 is fired at a time t O, the distance 8,, that the character must travel before contact with the print hammer is equal to the belt velocity V times the hammer flight time t,. Since t, is a function of voltage it would be desirable to make the belt velocity vary with the voltage in such a manner that S 8 remains constant with voltage, since the timing mark on the belt which initiates firing is at a set distance relative to the desired character.

Given the flight time versus voltage it is desirable that V B be such that SS /8V, is within acceptable limits over a range of voltage. For example if the belt velocity V varies linearly with the voltage V and the flight time t, varies hyperbolically with V, we have S V t K VK IV= K, K where K, and K are constants.

Therefore, SS ISV or S does not change with voltage.

The subject invention relates to a stepper motor belt drive scheme that provides automatic compensation for power supply voltage variations that affect print registration. As shown in FIG. 2 the print hammer 22 uses a work type magnet. One of the properties of such a hammer is its high sensitivity to input power. Curves a and b of FIG. show how flight time changes'when the input power is varied and how the impact velocity varies with input power. Variations in the supply voltage also cause an undesired variation in the flight time resulting in print misregistration. 1

According to the present invention the type belt 12 is driven by a stepping motor 30 whose velocity is dependent on the stepping rate, which in turn is controlled by a voltage sensitive oscillator 44 thus giving velocity proportional to voltage.

When the circuit 32 is first activated the base of the transistor 50 is held at a positive value by the ramp generator 52, blocking its conductivity. As the voltage of the ramp generator decays the transistor 50 is gradually turned over to the control of its base biasing circuit including the diodes D2, D and D11. The transistor 50 acts as a current source and the capacitor 48 is gradually charged and then discharged under the control of the relaxation oscillator 44. The charging rate of the capacitor 48 is determined by the diode resistor network in the base and emitter of the transistor 50. If the supply voltage increases the transistor 50 will be turned on harder by the'diode network. This will result in a faster charge and a higher frequency of oscillation of the oscillator 44. if the supply voltage drops, the oppomotor 30 is controlled in accordance with the value of the source voltage to which the conductors 28 are connected. Thus if the source voltage drops causing the print hammer 22 to have a longer flight time, the speed of the motor 30 is reduced so that the type character belt 12 moves at a slower rate, and proper registration of the print hammer 22 with the type characters 16 on the type belt is maintained. 1

From the above description and the accompanying drawing it will be apparent that the subject invention provides improved performance. Variations in source yoltage which previously by increasing the flight time of the print hammer caused misregistration of the print hammer and type characters is now compensated for by correspondingly changing the speed of the stepper motor 30 which drives the type belt so that the type characters arrive in timed relation with operation of the print hammer and misregistration is avoided.

While the invention has been described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein'without departing from the spirit and scope of the invention.

What is claimed is: 1. ln printing apparatus having a type carrier with a plurality of type characters thereon movable to present said type characters to different print positions along a print line of a document and having electromagnetically operated print hammer means disposed to be energized from a source of electrical energy for impacting the document and selected ones of said type characters to printon said document, said electromagnetically operated print hammers having a flight time which varies with the voltage of said source;

the improvement which comprises connecting a pulse operated motor whose speed varies with the frequency of the applied pulses to drive said type carrier, and connecting a voltage responsive variable frequency device whose frequency varies with the applied voltage to be energized from said source to generate pulses and connecting said device to said motor to thereby vary the speed of said motor for driving said motor, whereby changes in the flight time of said electromagnetically operated print hammer means with variations in source voltage are compensated for by corresponding changes in the speed of said type carrier so as to maintain proper registration under varying source voltage conditions between said print hammer means and type characters when impacting said document and selected type characters to print.

2. The invention as defined in claim 1 characterized by said voltage responsive frequency device comprising a relaxation oscillator connected in circuit with said motor through a pair of drive triggers.

3. The invention as defined in claim 2 characterized by a transistor connected to said source and to said oscillator to control the charging rate and hence frequency of a capacitor which determines the frequency of said relaxation oscillator.

4. The invention as defined in claim 3 characterized by a ramp circuit connected to said transistor to bias said transistor for delaying the buildup of said charging rate to a maximum when operation of the motor is initiated.

5. The invention as defined in claim 4 characterized by said drive triggers being connected to said motor through logic gate circuits. 

1. In printing apparatus having a type carrier with a plurality of type characters thereon movable to present said type characters to different print positions along a print line of a document and having electromagnetically operated print hammer means disposed to be energized from a source of electrical energy for impacting the document and selected ones of said type characters to print on said document, said electromagnetically operated print hammers having a flight time which varies with the voltage of said source; the improvement which comprises connecting a pulse operated motor whose speed varies with the frequency of the applied pulses to drive said type carrier, and connecting a voltage responsive variable frequency device whose frequency varies with the applied voltage to be energized from said source to generate pulses and connecting said device to said motor to thereby vary the speed of said motor for driving said motor, whereby changes in the flight time of said electromagnetically operated print hammer means with variations in source voltage are compensated for by corresponding changes in the speed of said type carrier so as to maintain proper registration under varying source voltage conditions between said print hammer means and type characters when impacting said document and selected type characters to print.
 2. The invention as defined in claim 1 characterized by said voltage responsive frequency device comprising a relaxation oscillator connected in circuit with said motor through a pair of drive triggers.
 3. The invention as defined in claim 2 characterized by a transistor connected to said source and to said oscillator to control the charging rate and hence frequency of a capacitor which determines the frequency of said relaxation oscillator.
 4. The invention as defined in claim 3 characterized by a ramp circuit connected to said transistor to bias said transistor for delaying the buildup of said charging rate to a maximum when operation of the motor is initiated.
 5. The invention as defined in claim 4 characterized by said drive triggers being connected to said motor through logic gate circuits. 